1. Field of the Invention
The present invention relates to a three-dimensional image processing apparatus that creates a three-dimensional image of a blood vessel from images before and after contrast medium injection.
2. Description of the Related Art
Blood vessels of a head extend in a complicated manner. For example, in a case of an aneurysm, in order to determine an optimal observation angle capable of confirming a neck of the aneurysm or obtain a relationship between the neck and a dome, or the aneurysm and the blood vessel/a capillary vessel near the aneurysm, 3D-DSA (three-dimensional digital subtraction angiography) is generally carried out.
In the 3D-DSA, the patient is repeatedly radiographed while rotating an X-ray tube around the patient, and a plurality of images each of which is obtained by radiographing the patient in a different direction are collected before or after contrast medium injection. Generally, a two-dimensional projection image, which is collected before contrast medium injection such that the blood vessel is not contrasted, is called a mask image, and a two-dimensional projection image, which is collected after the contrast medium injection such that the blood vessel is contrasted, is called a contrast image. By radiographing a subject at predetermined positions, an image before contrast medium injection and an image after the contrast medium injection are subtracted, so that the contrasted blood vessel portion is mainly extracted. In addition, a three-dimensional reconstruction process is performed on the extracted image of the blood vessel portion, so that a detailed three-dimensional image of the blood vessel is created. This three-dimensional image is called a 3D-DSA image.
As is widely known, the injection of the contrast medium imposes a negative side effect on the patient. In particular, at the time of an angiogram examination of a head, the moment the injection of the contrast medium starts, the patient may feel intense heat on his head, causing unbearable pain for the patient. As a result, the moment the contrast medium starts to be injected into the head of the patient, the patient moves his head. In order to prevent the patient from moving his head, the head of the patient is held in position by a belt. If the head of the patient is held in position tightly by the belt, the belt causes the patient to feel pain. Therefore, it is very difficult to completely prevent the patient from moving his head. Due to this reason, the biogenic positions in the frames are likely to deviate between the mask image and the contrast image. This positional deviation may appear on the 3D-DSA images as artifacts.
In order to reduce the artifact caused by the positional deviation, it has been considered that the positional deviation between the mask image and the contrast image is corrected and the subtraction is then performed between the mask image and the contrast image. However, actually, due to the positional deviation being a three-dimensional displacement, a reduction effect of the artifacts through the positional deviation correction is not very effective (for example, see JP-A-5-137711 and JP-A-2005-80285).